16S AMERICAN POMOLOGY. 



tempevainres. The manner in which cold acts upon plants 

 depends upon their physical structure. Lindley says, 

 freezing is attended with the following effects : — Tiie 

 fluids contained Avithin the cells of tissue are congealed 

 and expanded — ^tliis produces a laceration of the cell-walls, 

 and' impairs excitability by the unnatural extension to 

 which the cells are subjected ; the air is expelled from the 

 air-vessels and introduced into parts naturally intended to 

 contain only fluid ; the green coloring matter and other 

 secretions are decomposed, and the vital fluid or latex is 

 destroyed, and the action of its vessels is paralyzed. The 

 interior of the tubes, in which fluid is conveyed, is ob- 

 structed by a thickening of their sides. So we have as -a 

 result, both mechanical, chemical, and vital changes.* 



Our hardy fruit trees are woody perennials that hyber- 

 nate during th6 winter. Yet we find that even these suf- 

 fer upon some occasions from a great depression of tem- 

 perature ; it has been asserted that a certain degree of 

 cold would inevitably destroy the blossom buds at least, 

 and we often find that the bark is burst off from the wood, 

 and in some instances the wood itself is so injured as to 

 suffer from a kind of decomposition, and to become affect- 

 ed with a change generally known as the dry rot, losing 

 its elasticity and hardness, and acquiring a whitish color, 

 which is supposed may arise from the introduction of the 

 mycelia of fungous growths. Now it is believed that 

 these injuries do not arise so directly from the degree of 

 cold to which the tree has been exposed, as to the condi- 

 tion t)f its circulation at the time of the exposure. If the 



* Trans. Horticultural Society, London, Vol. II, p. 308 : and Am. Journal of 

 Science and Arts, March, 1840. 



